1. Field of the Invention
The present invention relates to an arm stopper mechanism that restricts the turning angle of a steering arm to which tie rods are respectively attached, and a steering apparatus using the same.
2. Description of Related Art
For example, in a saddle riding type vehicle such as an all terrain vehicle (ATV), a steering apparatus (particularly, a motor-driven power steering apparatus) is installed between a handlebar-side steering shaft and wheel (front wheel)-side steering members. The motor-driven power steering apparatus is an apparatus that applies the generated torque of an electric motor in assisting a steering force which a driver applies to handlebars.
The motor-driven power steering apparatus has built-in members such as an input shaft, a torsion bar, or an output shaft. The input shaft is connected to the handlebar-side steering shaft. The torsion bar is connected to the input and output shafts. A steering arm is attached to the output shaft (for example, refer to JP-A-2007-196927 (FIG. 2)).
The steering arm is the wheel (front wheel)-side steering members. The steering arm turns about the output shaft. The steering arm is provided with a tie rod hole for the attachment of a tie rod. The wheel is connected to the tie rod.
The motor-driven power steering apparatus is required to restrict the turning of the handlebars in order for a vehicle not to roll over in a lateral direction when the driver turns the handlebars to the maximum steering angle or greater in a clockwise direction or a counter-clockwise direction. Even though the driver may not turn the handlebars while the vehicle is traveling on a rough road, an external force caused by a protrusion (a convex portion) or the like on a road surface may be input to the motor-driven power steering apparatus and the handlebars via the wheel (the front wheel), and thus may cause the handlebars to be turned to the maximum steering angle or greater. Even in this case, the motor-driven power steering apparatus is required to restrict the turning of the handlebars in order for the vehicle not to roll over in the lateral direction. The motor-driven power steering apparatus is provided with an arm stopper mechanism as a mechanism for such a function which restricts the turning angle of the steering arm via a stopper.
The stopper is provided to protrude downward from a lower surface of a housing of the motor-driven power steering apparatus. When the driver turns the handlebars to the maximum steering angle or greater in the clockwise direction or the counter-clockwise direction, or when the input of an external force via the wheel (the front wheel) causes the handlebars to be turned to the maximum steering angle or greater, a striking surface provided in the steering arm strikes against a contact surface of the stopper. Accordingly, the arm stopper mechanism restricts the turning angle of the steering arm via the stopper, and thus the turning of the handlebars is restricted.
In this motor-driven power steering apparatus, when an increased bending load is applied to the output shaft, an excessive load may be applied to a bearing that supports the output shaft or the housing at the surroundings of the bearing. Accordingly, in the motor-driven power steering apparatus, it is desirable that a bending load be prevented from being applied to the output shaft.
However, in the related art, as will be described below, since the arm stopper mechanism of the motor-driven power steering apparatus is not configured so as to prevent a bending load from being applied to the output shaft, there is a problem in that a relatively large bending load may be applied to the output shaft.
For example, when one striking surface of the steering arm strikes against one contact surface of the stopper, a bending load vector is a value of a combined vector of an input load vector and a striking load vector. Here, the bending load vector is applied to the output shaft, thereby causing the output shaft to be bent, the input load vector is input from the wheel via the tie rod, and the striking load vector is applied to the contact surface of the steering arm from the stopper.
For this reason, a value of the bending load vector tends to increase as an angle formed by the respective directions of the input load vector and the striking load vector decreases. In contrast, a value of the bending load vector tends to decrease as an angle formed by the respective directions of the input load vector and the striking load vector increases.
Accordingly, for example, when an angle formed by the respective directions of the input load vector and the striking load vector is an acute angle (an angle greater than or equal to 0° and less than 90°), the bending load vector becomes a value greater than a value of the combined vector obtained when the input load vector is orthogonal to the striking load vector. In contrast, when an angle formed by the respective directions of the input load vector and the striking load vector is an obtuse angle (an angle of 90° to 180°), the bending load vector becomes a value smaller than or equal to a value of a combined vector which is obtained when the input load vector is orthogonal to the striking load vector.
When the striking surface of the steering arm is in contact with the contact surface of the stopper, the direction of the input load vector is determined by an attachment direction of the tie rod attached to the tie rod hole. The direction of the striking load vector is perpendicular to the striking surface (or the contact surface of the stopper) of the steering arm. Accordingly, the striking load vector is applied to a center position (hereinafter, referred to as a “striking center position”) of a contact portion between the striking surface of the steering arm and the contact surface of the stopper.
Here, a “center line of the entirety of the vehicle” refers to an imaginary straight line that passes through a center point in a lateral direction of the vehicle and extends in a longitudinal direction of the vehicle. A “starting point of contact surfaces” refers to a point at which the respective straight lines imaginarily disposed along two contact surfaces intersect each other on the center line of the entirety of the vehicle.
For example, in the arm stopper mechanism of the related art, an angle formed by two striking surfaces of the steering arm is set to be 180°, and an angle formed by two contact surfaces of the stopper is set to be 90° in such a manner that the angle (an angle between the two contact surfaces, and an angle formed in the stopper (for example, refer to an angle θst in FIG. 19B)) formed by the two contact surfaces of the stopper is smaller than the angle (an angle between the two striking surfaces and an angle formed in the steering arm (for example, refer to an angle θar in FIG. 18B)) formed by the two striking surfaces of the steering arm.
In the arm stopper mechanism of the related art, since an angle formed by the two contact surfaces of the stopper is set to be 90°, two striking center positions are respectively located at 45° rightward and leftward from the “center line of the entirety of the vehicle”, having the “respective starting points of the contact surfaces” as their centers.
In the arm stopper mechanism of the related art, when one striking surface of the steering arm strikes against one contact surface of the stopper, the striking load vector is applied to the striking center position in a direction oriented at 45° from the “center line of the entirety of the vehicle”. In the arm stopper mechanism of the related art, due to the attachment direction of the tie rod, the input load vector is applied to the surroundings of the tie rod hole in a direction in which an angle formed by the input load vector and the striking load vector becomes an acute angle (an angle greater than or equal to 0° and less than 90°).
In the related art, when configuring the arm stopper mechanism, an angle formed by the respective directions of the input load vector and the striking load vector is not taken into consideration as described above. For this reason, in the related art, in the motor-driven power steering apparatus using the arm stopper mechanism, a relatively large bending load may be applied to the output shaft, and at this time, an excessive load may be applied to the bearing that supports the output shaft or the housing at the surroundings of the bearing.
In this regard, the inventor of the present invention considers that since the bending load vector is a combined vector of the input load vector and the striking load vector, when the arm stopper mechanism is configured to cause the input load vector and the striking load vector to cancel out each other, it is possible to reduce occurrence of bending load.
The inventor of the present invention considers that when the arm stopper mechanism is configured to be opposite to the arm stopper mechanism of the related art in a relationship between an angle formed by the two contact surfaces of the stopper and an angle formed by the two striking surfaces of the steering arm (that is, in such a manner that an angle formed by the two contact surfaces of the stopper is greater than an angle formed by the two striking surfaces of the steering arm), and the angle formed by the two contact surfaces of the stopper is set to be greater than or equal to the angle (90°) of the arm stopper mechanism of the related art, it is possible to reduce occurrence of bending load.